Touch detection devices may come in various forms, such as, in the form of a touch key, a touch pad, or a touch screen, and may be classified into various types including infrared (IR) type, resistive type, ultrasonic type, induction type, and capacitive type, in terms of touch detection manner As shown in FIG. 1, in one typical touch detection device, a touch controller is connected to a touch sensor to collect and process touch detection data of the touch sensor so as to determine a coordinate of a touch point.
Sampling for touch detection data is usually performed on the detection nodes on a touch sensor in a scanning manner. For example, for a capacitive multipoint touch screen, the detection nodes are a plurality of projected capacitor nodes arranged in a matrix over a surface of the touch screen. For a group of touch keys, the detection nodes are respective sensors positioned in correspondence with the touch keys. The touch controller can obtain a matrix of desired sampling data within each detecting and sampling period by obtaining the sampling data by groups or individually. FIG. 2 illustrates a sampling data matrix obtained in a touch detection device with M*N nodes in one sampling period. In practice, most touch detection devices satisfy the condition of N+M≧3 except for the situation where a single touch key is used. Due to limited hardware resources and processing capability of the touch controller, to obtain this M*N sampling data matrix, scanning operations usually need to be performed by groups to achieve a sufficient refresh rate. The nodes may be grouped such that each group includes one or more rows of nodes, one or more columns of nodes, or nodes within a respective preset area. A typical example of such group sampling is arranged row by row, which results in the detection data as follows:
the first row: S11, S12, S13 . . . S1j . . . S1n 
the second row: S21, S22, S23 . . . S2j . . . S1n 
the i-th row: Si1, Si2, Si3 . . . Sij . . . Sin 
the m-th row: Sm1, Sm2, Sm3 . . . Smj . . . Smn 
According to the basic principle of touch detection, by detecting and data sampling when no touch event occurs, the touch detection device obtains a reference data matrix shown in FIG. 3 and stores the reference data matrix in a memory. New sampling data is then compared against the reference data to calculate the difference between the new sampling data and the reference data, as shown in FIG. 4A and FIG. 4B.Dij=Sij−Rij (where i=1, 2, . . . m; j=1, 2, . . . n)
Therefore, the sampling data sampled in each sampling period can be used to calculate a corresponding differential data matrix as the touch detection data for further processing, i.e. for determining whether a touch event occurred or calculating a coordinate or trajectory of a touch point. Exemplary calculating methods include threshold method, watershed method, center-of-gravity method, or the like. Whichever method is used, the detection data matrix is compared against a predetermined threshold value or threshold function to thereby determine whether a touch event occurred and whether the detected coordinate of the touch point is valid.
As can be seen from the above description, the reliability, stability and resolution of the touch detection results are dependent upon the precision and stability of the touch detection data. If the sampling value Sij includes a noise or error, this noise or error will be propagated to the differential value Dij, such that later calculations will produce an imprecise result.
However, all touch detection devices are subject to interferences during practical use, regardless of the form and detection manner of the touch detection devices. In many cases, the interferences introduce a large error into the touch detection data, which may degrade the stability and resolution of the touch detection result, or even worse, cause the touch detection device to produce a detection result of false touch or touch failure.
Take the currently popular capacitive touch screen as an example, in order to diminish the influence of LCD module and other outside interference signals, touch sensors with a double-layered or three-layered structure are generally required. The conductive layer closest to a display acts to shield the interference signals.
FIG. 5 illustrates an exemplary structure which includes a display 11, a housing 12, a driving electrode layer 13, a glass plate 14, a sensing electrode layer 15, and an outer panel 16. In this structure the driving electrodes need to be boldly filled and closely arranged over the entire touch sensor's area. During each scan, one or more driving electrodes are driven while the remaining driving electrodes are connected to ground. In this case, the driving electrodes also shield the interference signals.
FIG. 6A and FIG. 6B illustrate another structure in which driving electrodes 13 and sensing electrodes 15 are alternately arranged on the same plane. In this case, the driving electrodes 13 cannot be closely arranged to cover the sensing electrodes 15 and therefore cannot shield the interference signals. As such, an extra conductive shielding layer 24 is required in this structure.
The above described structures have the following defects. Firstly, these structures increase the difficulties in fabricating the sensor, which may decrease product yield and increase cost. In addition, the thickness of the sensor is increased thus increasing the weight as well as reducing the light transmittance thereof. Furthermore, only interference signals from below the sensor, for example, from the LCD display, can be shielded in these structures, while other interference signals, for example, power ripple, radio frequency, cannot be prevented.
There is currently another method of diminishing the interferences in which an auxiliary reference electrode is added to the sensor. It is configured such that this auxiliary reference electrode is only influenced by interference signals but not influenced by a touch. As such, the touch controller can eliminate the influence of outside interferences in theory by additionally sampling the reference electrode. However, this method would result in a complicated structure of the touch sensor and more detection ports of the touch controller being occupied, which increases the cost of the system.